The present invention relates to a process for producing a concrete mixture containing an AE (air entraining) fly ash cement (hereinafter called "AE fly ash concrete").
It has been already known in the art that AE fly ash concrete compositions have a wide variety of advantages such as providing improvement of workability in concreting, requiring less water for unit volume of concrete composition, enhancing the long term strength, improving both water tightness and durability, and reducing the heat of exothermic hydration resulting from a ball-bearing like effect of fly ash, the binding action of the cement components with the silicate contained in fly ash, the air-entraining effect by the addition of air-entraining agent, and the dilution effect of the cement components resulting from the addition of fly ash to concrete composition in combination.
Fly ash, however, contains an unspecified amount of unburnt carbon which absorbs the AE agent, thus resulting in a diminished AE effect and rendering it difficult to control the quantity of air to be entrained in fly ash concrete. For these reasons it is preferable to use fly ash having a minimum amount of unburnt carbon for fly ash concrete. This, however, is not readily available. If an producing AE fly ash concrete by using unburnt carbon-containing fly ash, for example an AE agent sold under the trade name of "Vinsol" by Yamaso Kagaku K. K. is added in the same ordinary amount specified by its producer to a fly ash concrete composition, the air content in the resulting concrete composition is far less than desired and thus no concrete composition containing the desired amount of air can be obtained. For this reason, as one way for ensuring that the desired amount of air is present in AE fly ash either 3 to 5 times the amount of AE agent in standard use is added by a trial-and-error method depending on the fluctuations in the quality and quantity of fly ash employed, or the amount of AE agent to be added is determined by previously confirming the amount of AE agent adsorbed by fly ash using the methylene blue absorption test. These methods, however, not only make the procedure very complex, but also give rise to a phenomenon of AE agent adsorption by unburnt carbon in the course of transport of the ready-mixed concrete by a truck-agitator resulting in the decrease of air in the ready-mixed concrete in combination with ordinary natural degassing. Thus the control of the amount of air in AE fly ash concrete composition is quite troublesome.